1. Field of the Invention
The present invention relates to a substrate treatment apparatus and a substrate treatment method for performing an etching treatment to etch a major surface of a substrate with an etching liquid. Examples of the substrate to be subjected to the etching treatment include semiconductor wafers, glass substrates for liquid crystal display devices, glass substrates for plasma display devices, substrates for FED (Field Emission Display) devices, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, and substrates for photo masks.
2. Description of Related Art
In semiconductor device production processes, a liquid treatment is often performed to treat a semiconductor wafer (hereinafter referred to simply as “wafer”) with a treatment liquid. An exemplary liquid treatment is an etching treatment which is performed by supplying an etching liquid to a major surface of the wafer. Examples of the etching treatment as herein defined include an etching treatment for patterning the major surface of the wafer (the wafer per se or a thin film formed on the wafer), and a cleaning treatment for removing foreign matter from the major surface of the wafer by utilizing an etching effect.
A substrate treatment apparatus for treating the major surface of the wafer with the treatment liquid is of a batch treatment type which is adapted to treat a plurality of wafers at a time, or of a single substrate treatment type which is adapted to treat a single wafer at a time. The substrate treatment apparatus of the single substrate treatment type includes, for example, a spin chuck which generally horizontally holds and rotates the wafer, a treatment liquid nozzle which supplies the treatment liquid toward the major surface of the wafer held by the spin chuck, and a nozzle movement mechanism which moves the treatment liquid nozzle above the wafer.
Where it is desired to perform the etching treatment on a device formation surface of the wafer to be formed with a device, for example, the wafer is held by the spin chuck with the device formation surface thereof facing up. Then, the etching liquid is spouted from the treatment liquid nozzle onto an upper surface of the wafer rotated by the spin chuck, while the treatment liquid nozzle is moved by the nozzle movement mechanism. As the treatment liquid nozzle is moved, a liquid application position at which the etching liquid is applied on the upper surface of the wafer is moved. The etching liquid spreads over the entire upper surface of the wafer by scanning the liquid application position between a rotation center and a peripheral edge of the wafer on the upper surface of the wafer (see, for example, Japanese Unexamined Patent Publication No. 2007-88381).
However, the etching liquid supplied to a center portion of the upper surface of the wafer receives a centrifugal force generated by the rotation of the wafer to be thereby moved radially outward on the upper surface of the wafer. Therefore, a peripheral portion of the upper surface of the wafer is subjected to an excess amount of the etching liquid which includes the etching liquid directly supplied thereto from the treatment liquid nozzle and the etching liquid moved thereto from the center portion of the upper surface. Thus, the peripheral portion of the upper surface of the wafer is etched at a higher etching rate than the center portion, resulting in uneven treatment of the upper surface of the wafer.
The etching liquid spouted from the treatment liquid nozzle is active immediately after being supplied onto the upper surface of the wafer, but is deactivated with time. Unless the deactivated etching liquid is properly replaced with newly supplied etching liquid on the upper surface of the wafer, the deactivated etching liquid and the newly supplied etching liquid are mixed with each other on the upper surface of the wafer, resulting in reduced etching power of the etching liquid. As a result, the etching rate is likely to be reduced on the entire upper surface of the wafer.
Particularly, where the etching treatment is performed on a major surface of a silicon wafer, the upper surface of the wafer has lower affinity for the etching liquid. Therefore, the etching liquid is liable to remain on the upper surface of the wafer to from a thick liquid film on the upper surface of the wafer. This makes it difficult to replace the etching liquid present on the upper surface of the wafer with the newly supplied etching liquid.
An etching reaction occurring when the major surface of the silicon wafer per se is etched is exothermic, so that the upper surface of the wafer is heated to a very high temperature by the etching treatment. This further promotes the etching treatment. However, the thick liquid film formed on the upper surface of the wafer removes heat from the wafer, whereby the temperature of the upper surface of the wafer is reduced. This further reduces the etching rate.